JPH0712646A - Photoelectric conversion circuit - Google Patents

Abstract

PURPOSE:To compose a photoelectric circuit provided with a battery consumption advance notice circuit, reduce the number of components and dissolve lowering of photoelectric conversion sensitivity due to the lowering of power source voltage. CONSTITUTION:A light emission part 32, a light receiving part 31 and an amplifier circuit 35 are provided as a photoelectric conversion circuit 30 having a battery consumption advance notice circuit, a resistor R1 is arranged between a power source and a common connection point (4) of the light emission part 32, the light receiving part 32 and the amplification circuit 35 and a decoupling capacitor C1 is placed between the common connection point (4) and a ground. And, when power source voltage of the resistor R1 and the circuit 35 becomes a specified value or less for the part 32, constitution is performed in that light emission control operation in which both ends voltage is regarded as light emission stop voltage is conducted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric conversion circuit which receives a signal transmitted by infrared rays and outputs a signal for detection.

[0002]

2. Description of the Related Art A variety of devices equipped with photoelectric conversion circuits are known, and as examples of the devices that utilize them, for example, audio signals from audio devices and audio signals from microphones are infrared-modulated and spatially transmitted to infrared signals. A system has been put into practical use in which a headphone or a speaker having a receiving unit (photoelectric conversion circuit) can receive this and listen to the wirelessly transmitted audio signal.

FIG. 3 shows an example of the system. Reference numeral 1 denotes an audio device such as a CD player or an audio amplifier. The L and R audio signals (AU _L , AU _R ) output from the audio device 1 are supplied to an infrared transmitter 2. In the infrared transmitter 2, for example, the voice signal (AU _L , AU _R ) from the infrared transmitter 3 is ± 150K at maximum.
2.3MHz and 2.8MHz subcarrier 2 frequency-modulated to Hz deviation
Outputs infrared rays that are amplitude-modulated (group-modulated) by waves.

On the other hand, a headphone 4 is provided as a receiving device for receiving this. Reference numeral 5 denotes a speaker unit. The headphone 4 is provided with a light-receiving unit 11 having a light-receiving element such as a silicon diode at a position to be a crown, for example, so that the transmitted infrared signal can be received. The infrared light received by the photoelectric conversion circuit including the silicon diode is an electrical signal (2.3MHz
It is amplified and output as a 2.8MHz subcarrier signal.

The signal output from the photoelectric conversion circuit is demodulated by the demodulation circuit mounted inside the headphone 4, and the demodulated L and R audio signals are supplied to the speaker drive circuit. Then, a drive signal is supplied from the speaker drive circuit to the speaker 5, and L and R sounds are output.

The headphone 4 is driven by 3 AA batteries at 3V, for example, and a light emitting section (battery consumption indicator) 21 for warning the battery consumption is provided.
Is provided, the light emitting operation of the light emitting unit 7 is stopped when the voltage of the battery becomes, for example, 2V, and the battery is preempted.

For example, FIG. 4 shows a photoelectric conversion circuit and a battery consumption advance notice circuit mounted in such a system. 8 in the figure
Is a battery part consisting of two manganese dry batteries, 10
Is a photoelectric conversion circuit, and 20 is a battery consumption warning circuit. In the photoelectric conversion circuit 10, the light receiving section 11 is composed of silicon diodes D ₁₁ and D ₁₂ . The plurality of silicon diodes are provided for the purpose of improving the light receiving sensitivity and realizing the light receiving directivity in all directions, and silicon diodes having different light receiving azimuth angles are connected in parallel. Of course, the light receiving element such as a silicon diode may be three units or more, or may be one unit if the device does not particularly require directivity.

Reference numeral 12 is a decoupling circuit including a resistor R ₁₄ and a capacitor C ₁₂ , and 13 is a decoupling circuit including a resistor R ₁₃ and a capacitor C ₁₁ . Reference numeral 14 is a circuit portion (hereinafter referred to as a BPF / matching circuit) that also serves as a bandpass filter and an impedance matcher, and includes coils L ₁₁ and L
_{It is} composed of ₁₂ , L ₁₃ and a capacitor C ₁₃ . This BP
The F / matching circuit 14 is provided for extracting the subcarriers of 2.3 MHz and 2.8 MHz from the electric signal received and detected by the light receiving unit 11 and output, and for impedance matching.

The bandpass filter is constructed so that natural light other than the transmitted signal component is received by the silicon diodes D ₁₁ and D ₁₂ ,
This is because the noise components of the silicon diodes D ₁₁ and D ₁₂ themselves as well as the interference signal to the received signal component are output from the light receiving unit 11.

Reference numeral 15 denotes an amplifier circuit, which amplifies the signal output from the BPF / matching circuit 14 and supplies it as an output S _out of the photoelectric conversion circuit 10 to a demodulation circuit in the subsequent stage (not shown).

On the other hand, the light emitting section 21 of the battery consumption advance notice circuit 20
Is provided with a light emitting diode D ₁₃ as a light emitting element, and a resistor R ₁₂ is arranged to flow a bypass current to the light emitting diode D ₁₃ . A resistor R ₁₁ is provided as a common load resistor for the current flowing through the light emitting diode D ₁₃ and the resistor R ₁₂ . In the low battery warning circuit 20, a battery portion potential at a point when the power supply voltage is lowered to 2V of 3V of 8, the light emitting diode D ₁₃ as is turned off, for example, the resistance R ₁₁ as follows, R ₁₂ resistance ratios are set.

Now, assume that the forward voltage drop (V _F ) of the light emitting diode D ₁₃ is 1.8 V and that the lighting current is 0.
Assume 5mA. Under this condition, the value of the load resistance R ₁₁ is set first. The voltage across resistor R ₁₁ is (power supply voltage -V
_F ) = 2.8V-1.8V = 1V. Therefore, the resistance value of the resistor R ₁₁ is: (voltage across R ₁₁ / D ₁₃ lighting current) = (1V / 0.5 mA) =
It becomes 2 kΩ, and for example, a 2.2 kΩ resistor is used.

[0013] Next-resistance path resistance value, i.e. the value of the resistor R ₁₂ is required, which, when the supply voltage becomes 2V, the voltage across the light emitting diode D _13, the light emitting diode D ₁₃ is fully The condition is to obtain a voltage of about 1.75 V at which the light is turned off, and under this condition, the current flowing through the light emitting diode D ₁₃ is zero.
_The condition for dividing the series voltage of ₁₁ and the side resistance R ₁₂ should be set as follows. That is, from (1.75V / 2V) = {R ₁₂ /(2.2kΩ+R ₁₂ )}, the resistance R ₁₂ ≈15.4kΩ, and for example, a resistor of 15kΩ is used. With such a configuration, the battery depletion notice circuit 20 can present the user with a battery depletion state by turning off the light emitting diode D ₁₃ .

[0014]

However, the photoelectric conversion circuit 10 and the battery depletion notice circuit 20 as described above have the following problems. First, the photoelectric conversion circuit 10
Since the battery consumption warning circuit 20 and the battery consumption warning circuit 20 are independently provided, there is a problem that the number of parts increases and the cost increases accordingly.

Furthermore, in the photoelectric conversion circuit 10, there is a problem that the photoelectric conversion sensitivity decreases as the battery is consumed. That is, since the points in FIG. 4 and the potentials at the points are almost proportional to the fluctuation of the power supply voltage, the power supply voltage supplied to the light receiving unit 11, the BPF / matching circuit 14, and the amplification unit 15 as the battery is consumed. Will decrease, and the operation of these circuits will be affected. In particular, the tuning operation is performed by parallel resonance between the junction capacitances of the silicon diodes D ₁₁ and D ₁₂ and the coil L ₁₁ , and the bandpass filter operation is realized, but the silicon diode D ₁₁ is accompanied by the decrease in the power supply voltage. If the junction capacitance of D ₁₂ , D ₁₂ increases, the tuning frequency will decrease, that is, the photoelectric conversion sensitivity will decrease.

[0016]

In view of the above problems, the present invention constitutes a photoelectric conversion circuit having a battery exhaustion notifying circuit to reduce the number of parts and to perform photoelectric conversion due to a decrease in power supply voltage. It is an object to realize a photoelectric conversion circuit which does not cause a decrease in sensitivity.

To this end, as a photoelectric conversion circuit, a light emitting means for indicating power consumption by stopping the light emitting operation, a light receiving means for detecting and outputting a signal by light reception, and an output of the light receiving means are amplified to form a signal output. The amplifier means, the light emitting means, the light receiving means, the resistance means arranged between the common connection point of the amplification means and the power source, and the decoupling capacitance means arranged between the common connection point and the ground are provided. . The light emitting means is configured such that the resistance means and the amplifying means perform a light emission control operation in which the voltage across the light emitting means becomes the light emission stop voltage when the power supply voltage becomes equal to or lower than a predetermined value.

[0018]

In the photoelectric conversion circuit having the above structure, the resistance means is used as both the decoupling resistance as the photoelectric conversion circuit and the load resistance in the battery consumption warning circuit, and the amplification means as the photoelectric conversion circuit emits light in the battery consumption warning circuit. Since it is used as a bypass resistance of the means, a photoelectric conversion circuit with a battery consumption warning circuit can be realized with a small number of parts.

Further, the potential at the common connection point of the light emitting means, the light receiving means and the amplifying means is kept substantially constant while the light emitting means is lit by the constant voltage characteristic of the forward voltage of the light emitting means. That is, the bias for the light receiving element in the light receiving unit and the amplification element in the amplification unit is fixed, and stable operation is realized.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the photoelectric conversion circuit of the present invention will be described with reference to FIGS. 1 is a block diagram of a photoelectric conversion circuit 30 with a battery consumption warning circuit, and FIG. 2 is a specific circuit diagram of the photoelectric conversion circuit 30 with a battery consumption warning circuit of FIG.

In these figures, 31 is a light-receiving portion formed by parallel connection of silicon diodes D ₁ and D ₂ for receiving infrared transmission signals, 32 is a light-emitting portion formed by a light-emitting diode D ₃ functioning as a battery exhaustion warning light, 33 is a decoupling circuit formed by a resistor R ₁ and a capacitor C ₁ ,
34 is a BPF / matching circuit including coils L ₁ and L ₂ and capacitors C ₂ and C ₃ , and 35 is a transistor Q ₁ . Q
_This is an amplifier circuit composed of ₂ , Q ₃ , resistors R ₂ , R ₃ , R ₄ , R ₅ , and a capacitor C ₄ .

The resistor R ₁ is composed of silicon diodes D ₁ and D
₂ , light emitting diode D ₃ , and transistors Q ₁ and Q
₂ and Q _{3 form} a common load resistance, and the capacitor C
Together with ₁ , form a decoupling circuit for each element.

The junction capacitance of the silicon diodes D ₁ and D ₂ and the coil L ₁ form a parallel resonance tuning circuit, and the coil L ₂ and the input capacitance of the transistor Q ₁ form a parallel resonance tuning circuit. . In this photoelectric conversion circuit 30, as described above, for example, 2.3 MHz and 2.8 MHz subcarriers are extracted as signals for infrared transmission and light reception detection, other interference signals are removed and extracted, and BPF / matching is performed to perform impedance matching. The circuit 34 is provided.

Therefore, the internal capacitance (about 50 pF) of the silicon diodes D ₁ and D ₂ and the coil L ₁ (27 μH)
And, it makes parallel resonance at 2.8MHz. In addition, the coil L ₂ (180 μH) and the input capacitance (about 15 pF) of the transistor Q ₁ cause parallel resonance at 2.3 MHz.

Then, these two resonance circuits are coupled by a capacitor C ₂ (22 pF) to form a bandpass filter having a pass band of 2 to 3 MHz, and at the same time, the parallel resonance described above causes impedance in the subcarrier frequency band of the diode system. By increasing the above, the photoelectric conversion efficiency of the infrared transmitted signal is improved. The capacitor C ₃ (0.01pF) is 2.
A low reactance DC blocking capacitor with negligible insertion loss for 3MHz and 2.8MHz.

The signal output from the BPF / matching circuit 34 is amplified by the amplifier circuit 35 and supplied as an output signal S _out of the photoelectric conversion circuit 30 to the demodulation circuit section in the subsequent stage.
Here, in the amplifier circuit 35, as the bias of the transistor Q ₁ , the emitter potential of the transistor Q ₃ is supplied in a direct current feedback manner through the resistor R ₃ , whereby the stability of each of the transistors Q ₁ , Q ₂ , Q ₃ is stabilized. I am working.

As described above, the light receiving section 31, the decoupling circuit 33, the BPF / matching circuit 34, and the amplifier circuit 35 realize the operation as a photoelectric conversion circuit. Then, in the photoelectric conversion circuit 30 with the battery consumption warning circuit, the operation as the battery consumption warning circuit is realized by the light emitting section 33, the decoupling circuit 33, and the amplification circuit 35.

Now, the forward voltage V of the light emitting diode D ₃ is
_{When F} is 1.8V and the power supply voltage of the 3V battery unit 8 drops to 2V, the light emitting diode D ₃ is turned off,
Suppose you want to set the warning for battery exhaustion.

First, in the battery consumption advance notice circuit, the current consumption of the amplifier circuit 35 corresponds to the bypass current to the light emitting diode D ₃ , and the resistance R is also set as described above.
₁ is the load resistance. Therefore, in order to realize the above-mentioned operation as the battery consumption notifying circuit in the case of this embodiment, when the power supply voltage becomes 2 V, the voltage across the light emitting diode D ₃ becomes the current consumption of the amplifier circuit 35. Resistance R ₁
The value of the resistor R ₁ may be set to be 1.75V by the voltage drop between the two.

Assuming that the current consumption in the amplifier circuit 35 is 0.57 mA, the resistance value of the resistor R ₁ is: resistance value = {(power supply voltage-extinguishing voltage) / (amplifier circuit current consumption)} = (2V-1.75 V) /0.57mA ≒ 440Ω, and the actually resistor R ₁ and to for example 470Ω resistor is used.

In the present embodiment thus set, the light emitting diode D ₃ functions as a battery consumption warning lamp, that is, an independent circuit system is unnecessary as a battery consumption warning circuit and is incorporated in the photoelectric conversion circuit. As a result, the number of components can be reduced and the circuit board size can be reduced, and the miniaturization and cost reduction can be promoted.

Further, points in FIG. 2 (light receiving portion 31,
The potential at the common connection point of the light emitting section 32 and the amplifier circuit 35 is substantially fixed by the value of the forward voltage drop V _F of the light emitting diode D ₃ until the power supply voltage of the battery section 8 drops to 2V. That is, due to the forward constant voltage characteristic of the light emitting diode D _3, the bias to the silicon diodes D ₁ and D ₂ and the transistors Q ₁ , Q ₂ and Q ₃ is kept constant, and the circuit operation is stabilized. In other words,
Until the power supply voltage drops to 3V to 2V, the tuning frequencies in the silicon diodes D ₁ and D ₂ and the BPF / matching circuit 34 do not shift, and it is possible to eliminate the decrease in sensitivity in response to the drop in the power supply voltage. .

The constants of the respective elements illustrated in the embodiments are examples, and the circuit configuration and constants are not limited to the embodiments. In any case, the terminal voltage of the light emitting diode D ₃ may be set to the extinction voltage by a dividing resistor or equivalent circuit means when the power supply voltage reaches the expected battery consumption warning voltage. Is. Therefore, the brightness (current value) of the light emitting diode D _{3 at} the time of lighting, the difference in forward voltage V _F due to the difference in product type, the series connection of a plurality of light emitting diodes, the series connection of the light emitting diode and the varistor, etc. The constants and the circuit configuration should be changed according to the implementation of equivalently increasing the forward voltage V _F.

The photoelectric conversion circuit of the present invention can be applied not only to acoustic devices such as so-called cordless headphones and cordless speakers but also to various other devices. Further, the present invention can be applied to a power supply which is relatively poorly regulated by an AC adapter or the like or a device which uses a power supply with a voltage drop.

[0035]

As described above, according to the present invention, the resistance means is used as both the decoupling resistance as the photoelectric conversion circuit and the load resistance in the battery consumption notice circuit, and the amplification means as the photoelectric conversion circuit is used as the battery consumption notice. By using it as a bypass resistance for the light emitting means in the circuit,
It is possible to realize a photoelectric conversion circuit with a battery consumption warning circuit with a small number of parts, and it is possible to promote miniaturization and cost reduction of the device.

Further, the potential at the common connection point of the light emitting means, the light receiving means, and the amplifying means is kept substantially constant while the light emitting means is lit by the constant voltage characteristic of the forward voltage of the light emitting means. There is also an effect that a bias is fixed to the light receiving element in the light receiving unit and the amplification element in the amplification unit, the photoelectric conversion sensitivity is prevented from being deteriorated due to the voltage drop, and stable operation is realized.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a photoelectric conversion circuit of the present invention.

FIG. 2 is a circuit diagram of an embodiment of a photoelectric conversion circuit of the present invention.

FIG. 3 is an explanatory diagram of a headphone system using infrared transmission.

FIG. 4 is a circuit diagram of a conventional photoelectric conversion circuit and a battery consumption advance notice circuit.

[Explanation of symbols]

30 Photoelectric conversion circuit 31 Light receiving part 32 Light emitting part 33 Decoupling circuit 34 BPF / matching circuit 35 Amplifying circuit D ₁ and D ₂ Silicon diode D ₃ Light emitting diode R _{1 to} R ₅ Resistance C _{1 to} C ₄ Capacitors L ₁ and L ₂ coil Q _1, Q _2, Q ₃ transistor

Claims (1)

[Claims] 1. A light emitting means for presenting power consumption by stopping the light emitting operation, a light receiving means for detecting and outputting a signal by receiving light, an amplifying means for amplifying an output of the light receiving means to output a signal, A resistance means arranged between a common connection point of the light emitting means, the light receiving means and the amplifying means and a power source, and a decoupling arranged between the common connection point of the light emitting means, the light receiving means and the amplifying means and the ground. A ring capacitance means, wherein the resistance means and the amplification means, with respect to the light emitting means, perform a light emission control operation in which the voltage across the light emitting means is a light emission stop voltage when the power supply voltage becomes a predetermined value or less. A photoelectric conversion circuit, which is configured to: